Electro-optic modulator with electrode interface region to improve signal propagation characteristics

An electro-optic modulator device includes a first optical waveguide region of a substrate and a second optical waveguide region of the substrate. The first optical waveguide region and the second optical waveguide region have crystalline structures. The electro-optic modulator device also includes a first electrode interface region of the substrate on a first side of the first optical waveguide region, a second electrode interface region of the substrate on a second side of the first optical waveguide region and on a first side of the second optical waveguide region, and a third electrode interface region on a second side of the second optical waveguide region. Each of the first electrode interface region, the second electrode interface region, and the third electrode interface region include material having a defective crystal structure or an amorphous structure.